While metal and plastic moulds are used to shape loaves and some other
comminuted meat products, natural and artificial casings are used as forms and
containers for sausages. The casings bind and protect the delicacy of the sausage
mixture; they regulate contraction and expansion of the sausage.

Sausages have historically been manufactured in natural casings. Natural casings are
almost exclusively prepared from different parts of the alimentary canal of pigs and
ruminants. Pig caings are derived from the stomachs, small intestines (pig casings,
smalls or rounds), large intestines (caps and middles) and terminal straight end of the
large intestines (bungs). Cattle casings are obtained from the oesophagus (weasands),
small intestines (rounds or runners), caecum (bungs), large intestines (middles) and
urinary bladders. Only the small intestines of sheep are used for sausage casings.

The walls of the entire intestinal tract consist of four distinct tissue layers: mucosa,
submucosa (rich in collagenous fibres), circular and longitudinal muscle layers and
serosa or external layer.

After separation from the adhering fat, the stomachs are
further processed in two ways. If the stomachs are to be incorporated into the sausage,
they are scalded and well cleaned. If they are to be used as casings, only a small
opening is made through which they are cleaned by flushing and then kept in salt until
used. Pig stomachs are used for stuffing head cheeses etc.

The pig's small intestines have an average length of
15 to 20 m and vary in diameter and strength according to the breed of animal and type
of feed consumed. Today fresh cleaning methods of processing casings without
fermentation are adopted.

After removal of fat and mesentery (“running”), cleaning and removal of the
intestinal contents (“stripping”) by machine or by hand, the intestines are first crushed
between rollers of a mucous crusher and then slimed, i.e. passed between a set of
rollers or strippers to remove mucosa and other unnecessary layers of the intestinal
wall (both muscle layers and serosa), leaving only the submucosa. The slimed
intestines are graded (inflated by air or water), salted with 40 percent salt and kept
until used.

The intestines of the pig (and particularly those of sheep) have long been processed
by fermentation. The process of fermentation enables their sliming by hand without
using machines. The method is as follows: after being turned inside out, the casings are
soaked in water at 20° to 24°C overnight or until the mucosa and muscle layers become
adequately tender to allow their manual removal (“sliming”). Such treatment causes the
processed pork rounds to be characteristically composed of only the submucosa layer;
the connective tissue-rich submucosa is not loosened and the final product is of good
mechanical strength.

After separation from the fat,
the large intestines are stripped of their contents, flushed out with water, turned over,
chilled in brine overnight, stripped free of mucosa and serosa, leaving the submucosa
and both muscle layers, and finally salted. The industrial term for the processed
caecum is “cap”; the first portion of the large intestines is not utilized as sausage
casings and the middle portion of the pig's large intestine is known as “middles”.

The pig's large intestines are also used for preparations as chitterlings or filler meat.
In sausage making, they are used for stuffing liver sausages, some salamis etc.

After the bungs (terminal end of large intestines, i.e. the ends of the
intestinal tract starting from the anus) are pulled free from their setting, they are
stripped under a spray of water which washes away the contents. The bungs are soon
afterward slimed, inflated for grading and thoroughly salted.

Pig bungs are 1 to 1.5 m in length. Their diameters vary from about 30 to more than
50 mm. Pig bungs are primarily used for liverwurst, cervelat, dry sausages etc.

After the musculature is removed from the outside
the weasands are washed turned inside out, cleaned, inflated with air, graded and
dried. They are used for large sausages; their length varies from 45 to 60 cm and over

The small intestines of cattle have an average length of 40 m the average diameter is 5 to 6 cm.

The rounds are turned inside out and slimed; the mucosa and serosa are removed
from the intestines leaving the submucosa and both smooth muscle layers which, in
beef intestines are much thicker than in pig intestines. After submerging in water and
washing, rounds are calibrated, tied and salted. Salted rounds are marketed in sets not
less than 100 yards (91.4 m) each set containing a maximum of five pieces. Beef rounds
are used for stuffing ring sausages, all beef sausages in Near East countries etc.

Beef rounds are classified in wide (38mm and over), medium (35 to 38 mm) and
narrow (35 mm and under).

The caecum or blind gut has an average length of 75cm and diameter of
12 cm. Caecums are substantially processed in the same way as beef middles. Beef
bungs are used for stuffing cooked sausages, capicola, large bologna etc. Their
diameter varies from 76 to 102 mm.

The middles are separated from the ruffle, flushed out with water,
trimmed free of fat, turned over, slimed and salted. Beef middles also include the
“straight” casing and are packed in sets each measuring about 17 m after salting and
composed of 5 pieces. Beef middles (narrow end, wide end and fat end) are used as
containers for different salamis and other large-diameter sausage products.

Beef bladders are washed, turned over and either salted or inflated
with air and dried. They are used for mortadellas, different sausage specialities etc.
Beef bladders are usually graded in large, medium and small sizes.

The small intestines (sheep or goat small casings or rounds) are pulled free of the
adhering fatty tissue, stripped free of their contents, immersed in water (10°C) and
fermented or directly slimed by machines. After the removal of the mucosa, serosa and
both muscular layers, the casings are chilled, inflated for grading, salted and stored.

Sheep casings are packaged in hanks (100 yards or 91.4 m) and may be extra wide
(25 mm and up), wide (22 to 24 mm), medium (20 to 22 mm), narrow-medium (18 to
20 mm) and narrow (16 to 18 mm). Sheep casings are primarily used for fresh frying
sausages and for frankfurters, wieners, chipolatas, etc. Sheep fore-stomachs are used
for haggis and some other meats and fancy meat specialties.

Sewn casings are made by sewing beef middles and small pig bungs together.
Special sewing machines are marketed for this purpose.

Sewn beef middles are made by sewing two or more pieces of beef middles
together. They are used for stuffing different fresh or semidry salamis, bologna etc.
They are made in different diameters with stuffing capacity from 0.7 to 2 kg.

Sewn pig bungs are usually manufactured in about 70 cm length with a diameter of
5.5 to 7 cm resulting in a stuffing capacity of 1.8 to 2 kg. Larger sizes of sewn pig bungs
are also sometimes made by sewing more than two pig bungs together.

All casings must be inspected before being used. The surface of all casings should
be completely free of any remaining adhering fat. All natural casings, except sheep
casings, before being used should be turned inside out, washed and trimmed of fat.
Salted casings should be soaked in water for desalting; dried casings are watered for
softening. Any casing that is left over the same day must be resalted.

Artificial casings offer a uniform cylindrical shape and the choice of any specific
diameter and suitable tensile strength as well as resistance to damage. They are filled
uniformly and, after filling, sausages can be linked by machine or by hand into
required lengths. The artificial casings are made from cellulose, collagen, plastic and
other materials.

Cellulose casings are manufactured in different sizes, ranging from 1.5 to 15 cm;
their important advantage is size uniformity. Cellulose casings are not soaked in water
prior to stuffing. Small diameter cellulose casings are produced in long lengths, but
large diameter fibrous cellulose casings are manufactured separately. Fibrous casings,
designed as special tough casings, are reinforced with cellulose fibres having great
strength as well as many of the attributes of natural casings; they take print well.
Special types of fibrous casings are the so-called easy-release and plastic-coated
moisture-proof casings. Dry sausage fibrous casings are especially developed for
semidry and dry sausages.

The interior surface of the cellulose casings can contain a water soluble dye which
colours the sausage surface during heat processing. Coloured cellulose casings in
cream, yellow, black and other colours are used for the cooked type of sausage. The
stuffed sausages have a smooth surface and the nature of the casing offers hygienic
protection for the sausage content.

Cellulose and other artificial casings are not as permeable to smoke as animal
casings. Stuffed cellulose casings cannot be pricked to expel air unless a red hot
needle is used. After the small casings are stuffed, they are twisted in the same way as
natural casings but with large casings the open end is twisted and then tied. Cellulose
casing for small diameter sausages should be peeled from the product by the sausage
manufacturer.

Regenerated collagen casings have many advantages and may be edible or
inedible. Edible collagen casings are stronger than natural casings. The inedible
collagen casings must be removed from the product before consumption.

Many types of plastic casings are available today. They are usually impermeable to
moisture and are sold under different names. The use of special grade smooth
polyethylene casings is another development in sausage production. Polyethylene
casings take print exceptionally well and permit an attractive presentation.

Impregnated cloth casings and other artificial casings are also used for stuffing
sausages.

The meat emulsion is extruded through the stuffing horn into natural or synthetic
casings mounted over the end of the stuffing horn.

Fig. 22 HAND LINKING OF SAUSAGES IS A SKILLFUL OPERATION

The large diameter casings are tied at one end, placed on the stuffing horn and the
sausage emulsion is ejected through the horn. The machine operator has to hold the
casing on the stuffing horn with one hand to restrict the flow off the horn while
operating the clipping or tying machine with his other hand. For linking small diameter
sausages 2 to 4 ply cotton thread is usually recommended while for tying very large
diameter sausages 10 to 16 ply thread may be necessary.

Cellulose casings for large sausages are first tied or clipped dry, soaked prior to
stuffing and then they are tied wet for the second closure. Fibrous casings are clipped
wet or dry at both ends.